Journal Article European XFEL serial crystallography FEL and synchrotron radiation Research Support, Non-U.S. Gov't XFEL instrumentation macromolecular crystallography single-particle imaging structural biology FEL physics Ferredoxins MHz X-ray microscopy MHz XFEL Metalloproteins Published Erratum Research Support, U.S. Gov't, Non-P.H.S. SFX X-ray diffraction X-ray free-electron laser X-ray free-electron lasers X-ray imaging X-ray phase contrast imaging X-ray scattering XFEL radiation aerosols aperture background scattering beam imaging coherent diffractive imaging